Neutronic reactor charging and discharging



July 14, 1959 5 w. H. zlNN v 2,894,892

v NEuTRoNIc REAcToR CHARGING AND DISCHARGING Filed'uay 15, 1951 s sheets-sheet 2 g BY W. H. ZINN NEUTRQNIC REACTOR CHARGING AND DISCHARGING Filevd Hay 15, 1951 July 14, 1959 s sheets-sheet :s

'n eazwey:

NEUTRoNfIc REACroRcH 'in GING A ND DISCHARGING Walter H. Zinn, Hinsdale, 4lll.,` assignor tov the United States of America as'represented by the United States Atomi'crEnergy Commission Application May 15, 1951, Serial No. 226,341

9' Claims; (Cl. 204e=193.2)

This invention'relates, generally', to a neutronic reactor cooled by a circulating liquid and more particularly to aY neutronic reactor wherein flssionable material about which a coolant liquid circulatescan be unloaded and reloaded with the assurance that coolant lluid will not spill or leak into the region adjacent to the reactor.

A fissionA chain reaction-v is achieved in a structure usually referred to as a pilef or neutronic reactor in a common type of which a plurality'oi:` bodies containingssionable material are geometrically disposed in a neu tronslowingy material termed the moderator. In one type of such" structure, the bodies of ssionable materiaflare arragedinparallel process tubes that extend through the modera-tor `from one side to the other. Since the iission vprocess isl an exothe'rmic reaction, the heat gen erated-by the nuclearactivity must be' dissipated in order tofmaintaina predetermined temperature level of operation.y This is usually accomplished by annexing a closed cooling system tothe reactor/whereby a cooling liquid is ilowedthrough a heat exchanger from which it moves to a reservoir where it is stored for recirculation through the tubes; Hence, the coolant ows about a closed system acquiring heat from the reactor and yielding it to the exchanger.

v Inasrnuch as the present invention is not concerned with the'- details of design and operation of a reactor, reference is herein made to the Fermi etal. Patent 2,708,656, dated May ,17, 1955,` in which detailed informationv is set forth regardingthe considerations of design and'operation of a reactor. n 4 Ina neutronic reactor employing liquid sodium or a liquid alloy of sodium and potassium metalsras the coolant circulatingin the cooling system, the problem of unloadiii'g"n reloading the bodies of tissionable material from the'reac'tor presentsa diiculty. The facts that Lrit. is radioactive and that such a metal or alloy dilyin an atmosphere "containing oxygen require t t no' spills'or leaks occur to endanger equipment or p'frsoiifriel.` It'hsf'been'found in accordance with' the present'invetion'thatcomplete 'isolation of the interior 'from the eiite`rior may Vbe'accornplished by using refrigeration ka valve'oif'freeze lock' for sealing the coolant lwithin thes'ystemfin such arnanner that a spill or leak is completely avoided. 'Ehe incorporation of the freeze lock greatlyfacilitates the unloading and reloading of a process tube of'the "reactorl overl the methods used heretofore, 'andinsures that therewill be no dripping Aof any kind.

Among-the other 'advantages inherent in the use of the presen vention afre the ease of operationfandy the lack of mo;` c n parts. yOther-a'ilvanta'ge's Will appear upon gofthe 4description ofthe invention illustrated in t rav'ving's, in which;

Figure' 1 isa "s'chenaticvev'v Aof a ineutro'nc reactor and 'a closed eooling'fsyst'em attached lthereto;

Figure, 2 is a 'horizontal I sectional AView of a lneutronic reactor;` i v l l Figure is avertical sectional viewl through a portion 2,894,89 n Patented July 14, 1959 2 of the reactor showing the geometric disposition -ofthe process tubes, taken'o'n the li'ne 3-3 of Fig'urevZ;VV

Figure 4 is an enlargedfragmentary vertical sectional View through one ofthe tubes shovvn in Figure 3, taken on the line 4-4 of Figure 3, showing a portion only of said tube and of an isolation chamber together with a! freeze lock; y c I Figure 5 is a transverse sectional View of the freeze lock taken on the line'S-S orf'Figure 4;

Figure 6 is an enlarged vertical sectional view of the freeze lock and the emptyV isolation charriber,y showing the" manner in which the coolant medium is disposed therein'y in the liquid state;

Figure 7 is an enlarged vertical sectionallview' oflthe' freeze lock and the' isolation chamber having a body ofV ssionable material dispfosed'withinl the coolingmediumf;

Figure 8 is apersp'ective View, partially in-fsection`,fof a portion of a iis'sionablebody;

Figure 9 is an enlarged transverseV sectionalvievvof the isolation chamber'and the ssionable body taken on7 the line 9 9 of Figure'7; and

Figure 10 is an'enlargedelevational view `ofthedischarge end ofthe-isolation chamber taken on the'line 10-10 of Figure 7p l Referring novir to Figure l a neutronic reactor is generally indicated at'V 20 together with a closed'coling system generally indicated at 22. The reactor 20"con'1 prises anv activeportionf24 anda dischargeV portion 26; At the end of the discharge portion 26 remotefrom the active portion 24 is disposed aY discharge coiiin or recep tacle generally` indicated at 28'.- v

Thecooling system 22 'comprisesa'coolantoutlet 32 and a coolant inletf`34gfaheat'exchanger 36, acoolant' reservoir 40,- and al coolant pump" 42. By virtue of the closed cooling system 22lattached to the` reactor 20,| a cooling medium or liquid 44 absorbsl heat Within thereA actor and yields it to the heat vexchanger 36, from which the liquid moves tothe reservoir40'an'd then returns to the reactor 20. A

Considering Figure 2," the reacto'rf'20 is shown in greater detail.4 In the principal or active-portion 24, there' are 'formed a'plurlity'o'f horizontal process chambers 46 within la modera'tr'48; which is an'elem'ent ofvlo'iv atomic weight, such aslcarbon orberyllium. In particularthis embodiment of thefneutr'oriic' reactor employs amoderator composed of beryllium-"bricks closely litted together. The bricks 'are milled'to,friritheelongated process chatn7 bers 46 when the' bricks `are laidk together. VIn' this manner'- the horizontalV process chambers'iexten'd from one end of theV moderatou48 to; the other. The cross-section of each chamber` 46` is"recta'gular.` In thisl manner each chamber accommodates an elongatedrectangular body or kslugf` as it is sometimes called, of iissionable material 50. EachV bodyStl'eXtends throughout one -chamber"46 Within the limits of the moderator 48;

The-body Sil has acore 52'of a tis'sion'able isotope', such as U235 or Pu', suitably diluted with inert, moderator, or absorber"` materials.` Asshown in Figure' 8, the core 52 is completely encased Within a surrounding jacket 54 of suitable'rn'a'teriall 'such as stainlesskstejel. A heat-conducting vbondff of sodiurne'potassium alloyfis disposed' betweenthe iission'able'mterial 52- and the jacket 54." The bond is liquidi andmustll all available space between the fls's'ionable 'material 5.2 and-the 'jacket 54.)V As the 'operating `temperature. of @the reactor increases; how? ever,- provision'forthefexpansion of this bondm'st bernade. Thisis donev bylmakin'gfthe steel jacket 54 enough so that it will bow suiciently togive the iri-v creased volume required.L In order' t'o-permit owof coolant past' the fuel element 50, the overall dimensions of the rectangular cross-section* of Ythe body 50 are slightly less than the crossfsection of the process chambers 46, and the body is held in position by longitudinal ribs 58 formed on the top and bottom surfaces of the body 50 as shown in Figure S. `The advantage of the use of rectangular or at bodies 50 is that at high temperatures appreciable expansion will occur within the jacket 54 which will be accommodated by` bulging of said jacket. A body having a` round cross-section will not accommodate any bulging but will rupture the jacket because its volume is `at a maximum with respect tothe enclosing surface area. i

Entirely surrounding theberyllium block moderator 48, which is cylindrical in structure, is acylindricaltank 60 that is fabricated of` a suitablematerial such asV steel. The tend of the tank 60 'nearest the loading portion 26 is covered by a at plate 62 which is perforated to accommodate a plurality of rectangular tubes 64 which communicate with the horizontal process chambers 46 'and which will be described more fully hereinafter.' The end of the tank 60 remote from theploading portion 26 is convex and houses the end section of the principal or active portion 24 into which `extend nozzles 66 from each chamber 46. yThe nozzles 66 have a cross-section slightly less than that of the chambers 46 and are constructed of a suitable material such as stainless steel sheet. In turn, said end section of thetank 60 communicatesuwith the coolent outlet 32 whichwas described hereinabove with reference to Figure 1. j v j Surrounding the cylindrical tank 60 is aflaminated shield generally indicated at `72 Athat consists `of layersA of steel members 74 and of a hydrocarbon 76,` such as oil. Extending through one side of the reactor are a nurn-` ber of control` rods` generally indicated at 78 that consist of a movable elongated member 80 passing through the laminated shield 72 and into the center of the principal or active portion 24 between certain of the process chambers 46 as shown by the dotted outline. Each meuk` bei' 80 is made of a neutron absorbing material, such as boron, and is designed to be cooled by an inert gas, such as helium, which circulates into and out of said control rods as shown by the arrows.

The loading portion 26 comprises a number of isolation chambers 82 equal to the number of process, chambers 46, anda shielded housing generally indicated at 84 surrounding `said chambers, consisting of a number of steel shield members 86. Each isolation chamber 82 constitutes an extension of an elongated channel which begins at the convex end of the steel tank 60 with the nozzles 66 and which includes the respective horizontal process chamber 46, the rectangular tube 64 connected V- With said chamber, a cylindrical pipe 88 connected to the tube 64 (see Figures 4, 6 and 7), and a circular casing 90. The tube 64 extends through the laminated shield 72 (Figure 2) to a weld 92 where the cross section of the channel enlarges like a funnel, from that of rectangle to a circle which is constituted by the pipe S8. As shown in Figures 3, 6V and 7, the pipe 88 extends to the larger circular casing 90 at which point there is a shoulder 94 where the pipe is welded at 93 to said casing.

Upon emerging from the laminated shield 72 the tubes i 64 extend through a compartment 96 which is formed by the shield members 86 of the housing 84 adjacent the outer s teel member 74 of the laminated shield 72. This compartment 96 is filled with inert gas througha conduit 98, thereby insuring the existence of an non-oxidiz ing atmosphere around the portion of the tubes 64 and the pipes 88 which are enclosed within said compartment. Within the compartment 96 an inlet port 100 forV the cooling liquid 44 is provided for each tube 64. As shown in Figure 3, said inlets communicate with a`secondary header 102 leading Vfrom a primary header 104 that, in turn, is'connected to the coolant inlet 34 which was described hereinabove with reference to Figure 1. As shown in Figure 4, a valve head 106 is provided to control the volume of cooling liquid 44 entering each port 100. Each valve head 106 may be manipulated to. and

' shielded housing 84.

from a valve seat 107 by an elongated rod 108 extending from said valve head to the `outer face of the structure, where it is accessible to operating personnel. The cooling liquid 44 fills the pipe 88 wherein it is conned relatively stagnant (closure of the outer end of the tube 88 being effected in a manner to be described). The cool ant ows through tube 64 to the chamber 46 in the active portion 24 of the reactor 20, whence it ows through the nozzles 66 to the coolant outlet 32.

On the pipe 88 between the inlet port 100 and the isolation chamber 82 is disposed` a freeze lock 110. As shown more particularly in Figures 4 and .5, the freeze lock 110 comprises an annular chamber 112 between the pipe 88 and a housing 114 attached'thereto in a fluid-tight manner.` At Y,one `side of the chamber 112 a partition 116 is disposed between a refrigerant inlet 118 and a refrigerant outlet 120. A refrigerant fluid 122 passes through the inlet '118, circulatesaround the pipe 88 within the chamber 112, and leaves said chamber via the outlet as shown by the arrows in Figure 5. As shown in Figure 2, the inlet 118 and the outlet 120 extend to a refrigeration unit 124 operated by an electric motor 126. Due to the possibilitygof leaks of cooling liquid 44 from the valve seat 107 and of refrigerant iluid 122, the freeze locks 110 are located in the compartment 96y which is filled with an inertgas, as above stated. i

Asshown in Figure 2, the isolation chambers 82 extend throughout the length of the shielded housing 84 to the end remote from the reactor 20. f Each isolation chamber 82 comprises (Figures 4, 6 7) the circular casing 90, an elongated sleeve or tube 128, and a refrigeration coil within said sleeve. The exterior surface of the casing 90 is completely surrounded `by the shield member 86 except for that end within the compartment 96. The sleeve 128 is `slidably disposed within, the Casing 90. Concentrically disposed within the sleeve 128 is an inner sleeve129 that is flared atv one end and Welded at 132 to the sleeve 128. As shown in Figures 6, 7 and 9 a refrigerationrcoil 130, disposed between the sleeves 128 and 129, is provided with an inlet port 134 and an outlet port 136 that extend from theV end of said coil remote from the shoulder 94. Each port 134 and 136 is provided with a union 138 and 140, respectively. A plug 142 is secured to `the end of the inner sleeve 129 in order to eiect closure thereof. The plug 142 is apertured centrally and is provided with packing 144 to accommodate an elongated shaft 146 `slidably disposed therein, one end of which is attachedV to the body 50 of iissionable material (Figure 7). In addition to sealing the inner sleeve 129 the plug 142 is provided with an annular ilange having a diameter equal t0 the inner diameter of the sleeve 128. Said ilange is apertured at two points to accommodate the ports 134 and 136 of the refrigeration coil 130 as shown in Figure 10. It is to be pointed outthat the end of the annular portion of the sleeve v128 `extends beyond the end of the inner sleeve 129 and also beyond the face of the In addition this end is provided with two notches 152 oppositely disposed which are adapted to accommodate a twist bar 154, the `purpose of which will be described hereinafter. Further, three lock members 156 are equidistantly disposed about the periphery of the sleeve 128 and attached to the face of the shield housing' 84 by detachable means,1such as bolts. The members 156 are secured against an annular flange 148 integral withthe sleeve 12,8` and are adapted to arrest any longitudinal movement of the sleeve 129 from the shoulder 94 at which pointis pro.- vided an annular gasket 158 of` a' suitable `material, such as aluminum to provide a seal against the cooling liquid 44 between the pipe 88 and said sleeve. Within the sleeve 129 are disposed two oppositely ,disposedsupport members 160 and 162 that support the body 50 of tissionable material lwhen it lodged therein.

The cask er receptacle 28 (Figure 2) constitutes a housing made of material v'of 'high atomic weight, "such asled, with 'an elongated chamber 166 centrally disposed along the longitudinal axis thereofand closed at the outer end. The rdimensions of said chamber are com parable both in diameter and length to those of the casing 90 forming the isolation chamber 82. Being designed as a cartridge receptacle for handling irradiated material, the cask 28 is adapted for endtoend abutment separately with the plurality of isolation chambers $2 i-norder to receive thesleeve128 containing `a body 5l) from the casing 90 (in a manner to be described). A pair of flexible refrigeration conduits168 and 170 extend through the chamber 166 and are adapted to be attached'to the unions 138 and 140, respectively, of the refrigeration coil 130. Since the end of the chamber '166 remote-from thcreactor 20 is closed, three apertures are provided, an aperture 171 centrally thereof for the elongated shaft -'146, and two, apertures 173 on either side thereof for the conduits 168 and 170, through Which said parts are slidably disposed. The conduits 168 nand 17h` llead to a refrigeration unit 172 whichv is attached to the Cask 28.

Operation The device illustrated permits unloading and replacinglbodies or slugs 50 of lissionable material without exposing "the cooling liquid 44 to the atmosphere, thereby safeguard-ing operating personnel from tire hazards and exposure to radioactivity. Under normal operating conditions, with the body 50 disposed within the several horizontal process chambers 46, as shown in Figure 2, the cooling liquid 44 circulates through said chambers `and over the surfaces of ,said bodies at ahigh fiow rate.. Duringfthis time the refrigerant fluid 122 is circulated about the annular chamber 112. of the freeze lock 110, serving to maintain a frozen mass 123 of coolantl 44Which effectively plugs the pipe 858 A(Figure 4),. At lcertain intervals of operation it becomes necessary to replace the bodies or slugs 50 with fresh 'supplies of 'ssionable material. At such times the frozen plug of cooling medium 44 is permitted to vmelt by Ythe simple expedient of shutting olf the circulation of the refrigerant fluid 122. The condition shown in AFigure 6 thenprevails, the cooling liquidV 44 filling the pipe 233 in addition to the inner sleeve 129 ofthe isolation chamber 82. vAt the Sametime the -rate of ilow ofY thel cooling mediumv 44 is regulated tov aA minimum necessary to carry olf the heat generated Vby induced 'radioactivity'. The body 50 to be'lre'placed is pulled from the horizontal process chamber A46 by means of the elongated shaft 146 through the tube 64 and the pipe 88 to the inner sleeve 129, as shown in Figure 7. The cask 28 is then aligned with the isolation chamber 82 and moved longitudinally towards it, the shaft 146 being slidably disposed through the aperture 171 in the end of said cask remote from the isolation chamber 82. However, before the cask 28 is tightly secured against the end of the chamber 32, the refrigeration conduits 168 and 170 are attached to the ports 134 and 136, respectively, of the refrigeration coil 1.3i) by means of the unions 138 and 146. The refrigeration units 124 and 172 are then activated to freeze the cooling liquid 44 within the freeze lock 110 and within the inner sleeve 129. In this manner the frozen mass 123 of cooling medium 44 extends from the freeze lock 110 to the remote end of the inner sleeve 129. This ensures no leakage or spilling of cooling liquid 44 when the sleeve 128 is Withdrawn from the casing 82 into the cask 28. Before the withdrawal can be accomplished, however, it is necessary to fracture the frozen mass 123 of cooling medium 44 by twisting the sleeve 128 within the casing 82. This is accomplished by detaching the lock members 156 and inserting the twist bar 154 into the oppositely disposed notches 152 in the end of `said sleeve. The force required to execute such a twist may be applied by an overhead crane (not illustrated) attached to the twist bar 154. The frozen 6, alloy of sodium and potassium severs with a clean fracture near the shoulder 94 of the isolation chamber 82. The sleeve 128 is then Withdrawn from the casing ,90 into, thel cask 28 by further retraction of the shaft 146. The cask 28 is then removed to another location where it is safe to melt the cooling liquid 44 and to removey the body 50 of ssionable material.

Loading afresh body 50 of iissionable material into the reactor 20 is the reverse of the removal of the spent body 50 as was set forth above. The cask 28is returned to its former position of abutment with the open end of the casing and the annular sleeve 128 is pushed into said casing until the annular gasket 158 on the forward end of the sleeve abuts the shoulder 94. The lock members- 1,56 are then xed in place and the refrigeration unit 124 is turned off in orderA to permit the frozen cooling liquid 44 to melt in the freeze lock 110. The pipe 8S' is then clear for the insertion of the fresh body 50 0f iissionable material to be thrust by means of the elongated shaft 146 into the horizontal process chamber 46 at the center of the reactor 20. The refrigeration -unit 1-24 is againv turned on to freeze the cooling liquid 44 at the freeze lock. After this the pumping pressure and flow rate of the cooling fluid 44 circulating through the particularprocess chamber 46* are readjusted to normal by means of the valve 106.

It will be understood that the above-described apparatus embodying the invention is merely by Way of illustration and.V not limitation, inasmuch as various and other forms of the invention will be readily apparent to those 'skilled in the art without departingfrom the spirit of the invention or the scope of the appended claims.

Whatlis claimed is: I

1. A method of removing a body of lissionable material from a neutronic reactor through a closed isolationchamber connected thereto-,while blocking the escape of substantial amounts of cooling uid comprising the steps of withdrawing the body into the chamber, freezingthe fluid at the end of the chamber adjacent the reactor, opening the chamber, and removing the body.

2. A method of removing a body of fissionable material from a process tube in a neutronic reactor -into "a closed isolation chamber connected thereto while vblocking the escape of substantial amounts of cooling liquid comprising the steps of withdrawing the body from the tube into the chamber, lfreezing the liquid at the end of the tubeV adjacent the chamber, opening the chamber at the end remote from the tube, and removing the body. Y

3. A neutronic reactor comprising an active portion having a plurality of process tubes, each tube having an open end adapted to accommodate bodies to be processed therein, a cooling liquid in the tubes, a liquid inlet near the open end, a liquid outlet near the other end, means for circulating the liquid through the tubes, a refrigeration unit around a segment of the tubes between the open end and the inlet, said unit being adapted to freeze the cooling liquid within the segment thereof an isolation chamber attached to the open end of each tube extending longitudinally therefrom and adapted to contain at least one body of fssionable material, and a second refrigeration unit around the chamber.

4. A neutronic reactor comprising an active portion having a plurality of process tubes, said tubes having an open end adapted to accommodate bodies to be processed therein, a cooling liquid in the tubes, a liquid inlet near one end of the tube, a liquid outlet near the other end, means for circulating the liquid through the tubes, a refrigeration unit around a segment of the tubes adjacent the open end, said unit being adapted to freeze the cooling liquid within the segment thereof, an isolation chamber attached to the open end of each tube extending longitudinally therefrom and adapted to contain at least one body of fssionable material, a second refrigeration unit around the chamber, and means for moving bodies between the tube and the chamber.

5. A neutronic reactor comprising an active portion having a plurality of horizontal process tubes, said tubes having an open end beyond the limit of the active portion adapted to accommodate bodies of iissionable material,

a cooling liquid in the tubes, a liquid inlet near the open end, a liquid outlet near the other end, means for circulating the liquid through the tubes, a refrigeration unit around a segment of each tube between the open end and the inlet, said unit being adapted to freeze the cooling liquid within the segment of the tube, an isolation chamber attached to said open end of each tube extending longitudinally therefrom and adapted to contain at least one body of lissionable material, and means for moving said bodies between the tubes and the chamber.

6. A neutronic reactor comprising an active portion, a plurality of horizontal process tubes extending through said portion, said tubes having an open end adapted to accommodate bodies of iissionable material, a cooling liquid in each tube,-a liquid inlet near theopen end, a liquid outlet near the other end, means for circulating the liquid through the tubes and over the surfaces of said bodies, a first refrigeration unit around a segment of keach tube between the open end and the inlet, an isolation chamber attached to the open end of each tube extending longitudinally therefrom, said chambers being adapted to receive bodies of Vfissionable material, means for moving said bodies between the tubes and the chamber, and a second refrigeration unit around the isolation chamber, said refrigeration units being operable to freeze the cooling liquid.

f 7. A neutronic reactor comprising an active portion having a plurality of horizontal process tubes, each tube having an `open end adapted to accommodate bodies of fissionable material, a cooling liquid in each tube, a liquid inlet near one end of each tube, a liquid outlet near the other end, means for circulating the liquid through the tubes, a refrigeration coil around a segment of the tube adjacent the open end and adapted to freeze the cooling liquid Within the-segment, an isolation chamber attachedto the open end of each tube extending longitudinally therefrom, and `a shaft slidably disposed through the chamber, one end of the shaft being `attachable to the body in each tube and being adapted to move said body between the tube and the chamber, said refrigeration coil being operable to freeze the cooling liquid.

8. A neutronic reactor comprising an active portion, a plurality of process tubes extending through said portion, said tubes having an open end adapted to accommodate bodies of fissionable material, a cooling liquid in the tube adapted to circulate therethrough and over the surfaces of said bodies, a liquid inletnear the open end of each tube, a liquid outletnear the other` end, a first refrigeration unit around a segment of each tube between the open end and the inlet, an isolation chamber attached to the open end of each tube extending longitudinally therefrom, said chamber being adapted to receive bodies of iissionable material, means for moving said bodies between the tube and the chamber, and a second refrigeration unit around the isolation chamber, said refrigeration units being operable to freeze the cooling liquid.

k9. A neutronic reactor comprising an active portion, a plurality of horizontal process tubes` extending through said portion, each tube having an open end adapted to accommodate bodies of lissionable material, a cooling liquid in each tube, a liquid inlet near the open end of each tube, a liquid outlet at the other end, means for circulating the liquid through the tube, a first refrigera tion coil around a segment of each tube between the open end and the inlet, an isolation chamber attached to the open end of each tube extending longitudinally therefromh, said chamber having a detachable inner portion com-1` municative with said open end, the inner portion being adapted to receive bodies of issionable material, the end of said portion remote from the chamber being closed and having anvaperture disposed centrally thereof, said chamber also having a second refrigeration coil around the inner portion, and a shaft slidably disposed in the aperture in a uid-tight manner and extendable through the chamber into the tube, one end of the shaft being at- Ltachable to the body in each tube and being adapted to move said body between the tube and the chamber, said refrigeration coils being operable to freeze the cooling liquid.

References Cited in the le of this patent UNITED STATES PATENTS Bennett Oct. 7, 1941 Young et al Oct. 23, 1951 OTHER REFERENCES 

1. A METHOD OF REMOVING A BODY OF FISSIONABLE MATERIAL FROM A NEUTRONIC REACTOR THROUGH A CLOSED ISOLATION CHAMBER CONNECTED THERETO WHILE BLOCKING THE ESCAPE OF SUBSTANTIAL AMOUNTS OF COOLING FLUID COMPRISING THE STEPS OF WITHDRAWING THE BODY INTO THE CHAMBER, FREEZING THE FLUID AT THE END OF THE CHAMBER ADJACENT THE REACTOR, OPENING THE CHAMBER, AND REMOVING THE BODY.
 7. A NEUTRONIC REACTOR COMPRISING AN ACTIVE PORTION HAVING A PLURALITY OF HORIZONTAL PROCESS TUBES, EACH TUBE HAVING AN OPEN END ADAPTED TO ACCOMMODATE BODIES OF FISSIONABLE MATERIAL, A COOLING LIQUID IN EACH TUBE, A LIQUID INLET NEAR ONE END OF EACH TUBE, A LIQUID OUTLET NEAR THE OTHER END, MEANS FOR CIRCULATING THE LIQUID THROUGH THE TUBES, A REFRIGERATION COIL AROUND A SEGMENT OF THE TUBE ADJACENT THE OPEN END AND ADAPTED TO FREEZE THE COOLING LIQUID WITHIN THE SEGMENT, AN ISOLATION CHAMBER ATTACHED TO THE OPEN END OF EACH TUBE EXTENDING LONGITUDINALLY THEREFROM, AND A SHAFT SLIDABLY DISPOSED THROUGH THE CHAMBER, ONE END OF THE SHAFT BEING ATTACHAABLE TO THE BODY IN EACH TUBE AND BEING ADAPTED TO MOVE SAID BODY BETWEEN THE TUBE AND THE CHAMBER, SAID REFRIGERATION COIL BEING OPERABLE TO FREEZE THE COOLING LIQUID. 